Majorana edge states in the s-wave kagome superconductor with Rashba interaction

We study a kagome lattice with on-site and extended s-wave superconducting pairing and show how the presence of Rashba spin-orbit (RSO) interaction leads to a (time-reversal symmetric) topological superconducting state that supports helical Majorana pairs at the boundary. We calculate the Z₂ topological invariant as a function of pairing parameters for different chemical potentials. The phase diagram at zero chemical potential reveals a topological superconducting state when the nearest-neighbor pairing strength dominates, and a trivial superconducting state otherwise. Away from zero chemical potential, a new nodal superconducting phase manifests, suppressing the topological state. When RSO interaction is absent in our model, the system becomes a trivial or nodal superconductor depending on the system parameters. A 2 X 2 time-reversal symmetry-breaking chiral flux phase has been shown to be energetically favorable in the AV₃Sb₅ kagome family [1,2]. To this end, we incorporate such symmetry-breaking order in our model, leading to chiral Majorana edge states characterized by a Chern number. We show how the RSO interaction allows for topological phases with distinct Chern numbers for different system parameters. These results motivate the exploration of Majorana fermions in the recently discovered kagome superconductors.

[1] Feng, X., Jiang, K., Wang, Z., & Hu, J. (2021). Chiral flux phase in the Kagome superconductor AV₃Sb₅. Science bulletin, 66(14), 1384-1388.

[2] Denner, M. M., Thomale, R., & Neupert, T. (2021). Analysis of charge order in the kagome metal AV₃Sb₅ (A= K, Rb, Cs). Physical Review Letters, 127(21), 217601.